[3] Gilles is the younger brother of French actress Marie-France Pisier.

Pisier has obtained many fundamental results in various parts of mathematical analysis.

Using probability in vector spaces, Pisier proved that super-reflexive Banach spaces can be renormed with the modulus of uniform convexity having "power type".

In the theory of C*-algebras, he solved, jointly with Marius Junge, the problem of the uniqueness of C* -norms on the tensor product of two copies of B(H), the bounded linear operators on a Hilbert space H. He and Junge were able to produce two such tensor norms that are nonequivalent.

[3] In 1997, he constructed an operator that was polynomially bounded but not similar to a contraction, answering a famous question of Paul Halmos.